1. Technical Field
The present invention relates to a mount structure that is formed by mounting an electronic component on a substrate. The present invention further relates to an electro-optical device that adopts the configuration of such a mount structure, and an electronic apparatus that is provided with such an electro-optical device.
2. Related Art
As a typical configuration of a mount structure that is known in the technical field to which the present invention pertains, an electronic component such as an IC is mounted on a substrate by means of a chip-on-glass (hereafter abbreviated as “COG”) method or the like with an anisotropic conductive film (hereafter abbreviated as “ACF”) being interposed therebetween. In the formation of such a mount structure, an ACF having resinous particles and an electro-conductive film (i.e., metal plating layer) that coats the resinous particles is commonly used in the related art. When manufacturing a liquid crystal device, which is an example of an electro-optical device that has the common/popular mount structure described above, an electronic component for driving liquid crystal elements (e.g., driver IC) is mounted on a substrate with an ACF interposed therebetween. The COG method or a similar method is used for the mounting of the electronic component thereon.
In the configuration of such a mount structure, the input/output terminals (i.e., bumps) of the driver IC are electrically connected to source electrodes to which data signals are supplied, gate electrodes to which scanning signals are supplied, and external connection electrodes, respectively, which are formed on the substrate. Specifically, the input/output terminals of the driver IC are electrically connected thereto via electrically conductive particles that are provided in a random layout in an ACF adhesive. As described above, electro-conductive particles contained in an ACF play an important role in electrically connecting the terminals of an electronic component and various kinds of electrodes.
These days, there is a growing demand for a liquid crystal device that is capable of offering high-definition image display. As the market demands for the higher definition of display, the pitch of the terminals of an electronic component is becoming narrower and narrower. The same holds true for electrodes formed on a substrate. Because of the narrowed pitch of the terminals/electrodes, the electric connection method of the related art that uses an ACF has a disadvantage in that a short circuit failure could occur between adjacent terminals or adjacent electrodes via electro-conductive particles contained in the ACF.
In order to provide a technical solution to the problem of such a short circuit failure, JP-A-2005-353983 proposes an alternative electric connection method that does not use any ACF at all.
In the proposed electric connection method, each terminal of an electronic component is made up of an electrode pad, a resinous projection having elasticity, and an electro-conductive film that covers a part of the surface of the electrode pad to extend across (i.e., further cover) the surface of the resinous projection. Having such a configuration, the electronic component disclosed in the above-identified patent publication is adhered to a substrate by means of an ordinary non-special adhesive with each of the electro-conductive films being directly connected to the corresponding one of various kinds of electrodes.
Since the proposed configuration does not employ any electro-conductive particles, it is possible to prevent adjacent terminals or adjacent electrodes from being short-circuited with each other. As another advantage, even when the bonding strength of the adhesive decrease due to aging, that is, with the passage of time, after mounting of the electronic component on the substrate, the resinous projection gets elastically deformed in counteraction to the decrease in the adhesive strength; and therefore, thanks to the resilience force thereof, there rarely occurs an electric connection failure between the electro-conductive film and the electrode. As still another advantage, the cost of production is reduced because electro-conductive particles are not used. As explained above, the proposed electric connection method offers various advantages over the conventional electric connection method that uses ACFs.
In the electric connection method described in the above-identified patent publication, it is possible to make a judgment as to whether the electric connection between a certain terminal of an electronic component and the corresponding electrode is in a good condition or in a poor condition on the basis of amount of deformation of the terminal caused at the time when the electronic component is non-tentatively mounted on a substrate. Specifically, it is possible to judge that the electric connection between a certain terminal of an electronic component and the corresponding electrode is in a good condition if the terminal is elastically deformed by a predetermined deformation amount, where a sufficient degree of deformation thereof means that the contact area between the electro-conductive film of the terminal and the electrode is not insufficiently small. However, it is practically difficult to visually perceive the amount of deformation of a terminal after the non-tentative mounting of an electronic component on a substrate because the terminal is arrayed at a position that overlaps the corresponding electrode when viewed in two dimensions (i.e., in plan view). That is, the proposed electric connection method has not addressed the problem of practical difficulty in visually checking whether the electric connection between a certain terminal of an electronic component and the corresponding electrode is in a good condition or in a poor condition.
In the ACF-based electrical connection method used in the related art that is described before the above alternative proposed method, a judgment as to whether the electric connection between a certain terminal of an electronic component and the corresponding electrode is in a good condition or in a poor condition is made as follows. After the non-tentative mounting of an electronic component on a substrate that has transparency, each shape of deformation of several test-target ACFs, which are selected among a plurality of ACFs placed in a random layout in the mounting area of the electronic component, is visually observed through the transparent substrate. Then, each shape of deformation of the visually-checked target ACFs is indirectly compared with more than one specified shapes of deformation thereof that have been stored and registered in, for example, a personal computer or the like in advance as sample deformation shapes. The plural shapes of deformation thereof are pre-defined in the personal computer or the like so as to enable rank classification for the check target ACF (e.g., a good deformation shape, a poor deformation shape, and the like) in a comparative manner. This is how the judgment is made in the first-mentioned electrical connection method that uses ACFs. According to such an electric connection condition check method, it is not possible to visually observe the state of electric connection therebetween by means of a mount structure only in an easy manner.